Abstract

Diffusion of inorganic nitrogen (N) depends on the physical capacity of the soil to store and its hydraulics properties to transport nutrients in time and space. Therefore, continuous drying and wetting cycles affect the availability of mineral N in the soil profile. The objective of this research was to simulate the diffusive flow of inorganic N from the physical N store of two volcanic soils after rewetting, using the microdialysis technique. Undisturbed soil cores at four depths (0-20; 20-40; 40-70; 70-100 cm) in two volcanic soils (Andisol and Ultisol) were collected. Diffusive N fluxes were determinate during three drying and rewetting cycles (0 to 100 kPa) using a microdialysis technique. Volumetric water content (VWC) at each matric potential was calculated. Diffusive N fluxes of inorganic forms NO2- and NH4+ were not different (p > 0.05) between the soils during cycles, in a range of 3 - 11 nmol N cm-2 h-1. However, the diffusive N flux in form of NO3- in the soil after first rewetting, increase 30 times in Andisol from 81.1 ± 72.2 to 3183.5 ± 1119.0 nmol N cm-2 h-1(34 to 62% VWC) and 150 times in Ultisol, from 55.8 ± 20.2 to 8411.0 ± 2130.6 nmol N cm-2 h-1(31 to 58% VWC) in the first 20 cm of depth. In addition, the diffusive nitrate fluxes decrease in depth in both soils, through cycles. Therefore, the available nitrate in soil presents different times of permanence depending on the porous system’s functionality and soil water content.